Method and apparatus for detecting the presence of a web within a web dryer

Abstract

A method and apparatus for reliably detecting the occurrence of a web break in a web processing system is disclosed employing a non-contacting, non-optical sensor to detect the presence of the web. Cushion pressure in a cushion pressure zone adjacent the web is sensed to determine a web break condition. A sensor block is mounted within an enclosure through which the web passes. The sensor block is configured to sense the cushion pressure in the region between an air bar and the web. The cushion pressure is communicated outside the enclosure to a transducer which compares the cushion pressure to either the internal ambient pressure of the enclosure or to atmospheric pressure. The resulting differential pressure is compared to a threshold differential; if the measured differential pressure drops below the predetermined threshold pressure, a web break is indicated and web processing is terminated.

I claim: 
     
       1. An apparatus for detecting a break in a web in a web offset printing system, the apparatus comprising: an enclosure, said enclosure having an interior, an entrance aperture and an exit aperture, said interior being intermediate said entrance aperture and said exit aperture, said web traversing said interior from said entrance aperture to said exit aperture;   a fluid pressure means within said interior for providing a fluid flow within said interior, said fluid pressure means providing at least one inlet to said interior and providing at least one outlet from said interior for establishing said fluid flow, said at least one outlet meeting said interior at an outlet boundary, said fluid flow generally flowing from said at least one inlet, through a cushion pressure zone at a surface of said web within said interior, and through said at least one outlet past said outlet boundary and creating a cushion pressure in said cushion pressure zone; and   a sensing means for sensing pressure, said sensing means being disposed to sense said cushion pressure substantially at said outlet boundary.   
     
     
       2. An apparatus for detecting a break in a web as recited in claim 1 wherein said sensing means comprises a sensor and a communication means for communicating pressure, said sensor being situated outside said enclosure, said communication means communicating said cushion pressure from within said interior substantially at said outlet boundary to said sensor. 
     
     
       3. An apparatus for detecting a break in a web as recited in claim 2 wherein said communication means comprises a conduit. 
     
     
       4. An apparatus for detecting a break in a web as recited in claim 3 wherein said communication means further comprises a block means for locating said conduit substantially adjacent said outlet boundary; said block means including fixing means for fixing said block means with respect to said fluid pressure means, said block means being adjustably fixable by said fixing means with respect to at least one selected outlet of said at least one outlet. 
     
     
       5. A method for detecting a web break in a web fed printing press, the method comprising the steps of: guiding said web through an enclosure, said enclosure defining an interior intermediate an entrance aperture and an exit aperture, said web traversing said interior from said entrance aperture to said exit aperture;   providing a fluid pressure means within said interior for generating a fluid flow within said interior, said fluid pressure means having at least one inlet to said interior and at least one outlet from said interior for establishing said fluid flow, said at least one outlet meeting said interior at an outlet boundary, said fluid flow generally flowing from said at least one inlet through a cushion pressure zone at a surface of said web within said interior, and through said at least one outlet past said outlet boundary and creating a cushion pressure in said cushion pressure zone; and   sensing said cushion pressure substantially adjacent said outlet boundary.   
     
     
       6. A method for detecting a web break in a web fed printing press as recited in claim 5 wherein said sensing is effected by a sensing means, said sensing means comprising a sensor and a communication means for communicating pressure, said sensor being situated outside said enclosure, said communication means communicating said cushion pressure from within said interior substantially adjacent said outlet boundary to said sensor. 
     
     
       7. A method for detecting a web break in a web fed printing press as recited in claim 6 wherein said communications means comprises a tube. 
     
     
       8. A method for detecting a web break in a web processing system, the method comprising the steps of: (1) guiding said web through an enclosure, said enclosure defining an interior intermediate an entrance aperture and an exit aperture, said web traversing said interior from said entrance aperture to said exit aperture;   (2) providing a fluid flow means within said interior for establishing a fluid flow within said interior, said fluid flow means including at least one inlet to said interior and at least one outlet from said interior, said at least one outlet meeting said interior at an outlet boundary, said fluid flow generally flowing from said at least one inlet through a cushion pressure zone at a surface of said web within said interior, and through said at least one outlet past said outlet boundary, creating a cushion pressure in said cushion pressure zone; and   (3) sensing said cushion pressure substantially at said outlet boundary to detect said break.   
     
     
       9. An apparatus for detecting a break in a web in a web offset printing system, the apparatus comprising: an enclosure, said enclosure having an interior, an entrance aperture and an exit aperture, said interior being intermediate said entrance aperture and said exit aperture, said web traversing said interior from said entrance aperture to said exit aperture;   a fluid means within said interior for providing a fluid flow within said interior, said fluid pressure means providing at least one inlet to said interior and providing at least one outlet from said interior for establishing said fluid flow, said at least one outlet meeting said interior at an outlet boundary, said fluid flow generally flowing from said at least one inlet, through a cushion pressure zone at a surface of said web within said interior, and through said at least one outlet past said outlet boundary and creating a cushion pressure in said cushion pressure zone; and   a sensing means for sensing pressure, said sensing means being disposed to sense said cushion pressure substantially at said outlet boundary;   said sensing means comprising a sensor and a communication means for communicating pressure, said sensor being situated outside said enclosure, said communication means communicating said cushion pressure from within said interior substantially at said outlet boundary to said sensor;   said communication means comprising a conduit and a block means for locating said conduit substantially adjacent said outlet boundary; said block means including fixing means for fixing said block means with respect to said fluid pressure means, said block means being adjustably fixable by said fixing means with respect to at least one selected outlet of said at least one outlet.